This invention relates to saw chain grinders. More particularly, the invention relates to a method and machine for automatically grinding or sharpening the surfaces of cutter links of a saw chain.
Various types of saw chain grinders have been used for many years. Many of these grinders utilize a rotatably mounted grinding wheel which is adapted to be positioned adjacent the surface to be sharpened, such as that of a cutter tooth, and wherein movement of the cutter tooth into the grinding wheel is effected by manual displacement of a saw chain carriage to which the saw chain is mounted. Such machines are shown in my previous U.S. Pat. Nos. 3,349,645; 3,695,123; and 3,779,103. Alternatively, some machines oscillate the grinding wheel into the cutter tooth. See U.S. Pat. Nos. 4,104,793 and 4,044,635. While the machines disclosed in these patents may be effective in accurately sharpening individual cutter teeth of a saw chain, the sharpening process may be relatively time-consuming if all of the cutter teeth of the saw chain are to be sharpened. This is because the saw chain must be manually advanced to the next cutter tooth after each tooth is ground. Another drawback with some of the prior art grinders is that there is no guarantee that each of the cutter teeth will be sharpened in precisely the same fashion or to the same extent as the other cutter teeth of the saw chain.
There have been prior attempts to automate the grinding operation. One example is disclosed in U.S. Pat. No. 3,890,857 to Simington. This patent describes a machine in which the saw chain is intermittently indexed to move consecutive cutter teeth on one side of a saw chain into position proximate the grinding wheel for grinding thereof. More specifically, a pair of spaced saw chain holder wheels are included, one of which is rotatably mounted adjacent one end of an axially reciprocable rod which extends across the machine to opposite sides of a grinding wheel. The second holder wheel is mounted in spaced relation with the first holder wheel to permit a saw chain to be mounted to and extend between the two holder wheels. The rod is driven in an axial direction by a first motor to move the saw chain on the first holder wheel into the side edge of the grinding wheel. The rod then reverses its direction and moves that holder wheel away from the grinding wheel. The movement away from the grinding wheel actuates a switch which starts a second motor mounted in driving connection with the second holder wheel. This second motor rotates the holder wheels to advance the saw chain until the next cutter tooth contacts an abutment flange positioned adjacent the first holder wheel. Once this takes place, the rod reverses its direction and moves the first holder wheel and this next cutter tooth toward the side of the grinding wheel. The movement of the rod back toward the grinding wheel actuates a switch which stops the second motor. However, until this second motor is shut down, the second holder wheel continues to be driven by the second motor, thus resulting in slippage between the saw chain and the second holder wheel. This slippage occurs because the saw chain is held in place by the contact between the cutter tooth to be sharpened and the abutment flange. Once this second cutter tooth contacts and is sharpened by the grinding wheel, the rod reverses and the process is repeated until all the cutter teeth on one side of the saw chain are sharpened. The saw chain is then removed from the chain holder wheels on the one side of the grinding wheel and is mounted between the holder wheels on the opposite side of the grinding wheel to grind the cutter teeth on that side of the saw chain.
While Simington's machine at least theoretically provides automated means for consecutively sharpening all of the cutter teeth on a saw chain, it exhibits a number of drawbacks. First, Simington's machine necessitates the use of two separate motors in addition to the grinder motor. This not only increases the initial expense but also the operating expense to use the machine. Second, Simington depends upon a certain amount of slippage between the saw chain and his holder wheels. Such slippage not only results in a substantial waste of output of the second motor, but also requires that the saw chain be precisely fit to the holder wheels such that the requisite amount of slippage will take place only when desired, and that such slippage will occur without overloading the second motor. Another disadvantage inherent in Simington's indexing operation is that the only way that Simington provides for adjustment of the grinder to accommodate saw chains having differing pitches between the cutter teeth is to either increase or decrease the amount of slippage between the holder wheels and the saw chain. Another disadvantage of Simington's indexing operation is that it requires that his second motor be started and stopped for each cutter tooth. This type of operation naturally results in a dramatically shortened life for the motor and also results in a high degree of wear and therefore shortened life for the switches involved. Yet another drawback of this prior art machine is that there is no means provided for regulating the speed at which the cutter tooth is directed into the grinding wheel, which may sometimes be desirable in the event the cutter teeth are excessively worn or if they only have a small amount of cutting tooth remaining. One more drawback is that his grinding wheel gradually moves across the cutter tooth surface rather than grinding the entire surface at once. This may promote uneven wear of the grinding wheel. A final drawback which is, in effect, the cause of some of the aforementioned problems, is that Simington's machine requires movement of the saw chain along two planes of movement at right angles to one another. As noted above, this greatly affects the complexity of the machine and reduces its efficiency.
My U.S. Pat. No. 3,717,051 is directed to a saw chain depth gauge grinder which includes means for automatically indexing the saw chain as consecutive depth gauges are ground. In this grinder the depth gauges themselves actually act as cams to reciprocate the grinding wheel between active grinding and inactive positions. Because of the fact that the indexing of the saw chain is substantially continuous, with indexing continuing even when the grinding wheel is in a lowered, active position, this grinder is limited to use as a depth gauge grinder and is not adaptable for use in grinding other surfaces, i.e., gullets and cutter teeth.
Hence, it is a primary object of the present invention to provide an improved saw chain grinder which effectively and reliably overcomes the aforementioned drawbacks and limitations of the prior art proposals. More specifically, the present invention has as its objects one or more of the following taken individually or in combination:
(1) The provision of an automatic saw chain grinder and a method for grinding saw chains which necessitates the use of only a single motor in addition to the grinding wheel motor, and which is operable with a minimum of wasted movements and power requirements, and which therefore exhibits low initial and operating costs;
(2) To provide an automatic saw chain grinder wherein the amount of cutter tooth which is ground off is easily adjustable, and which will provide for the same amount of grinding taking place on each of the cutter teeth of a saw chain;
(3) To develop a saw chain grinder which is highly versatile in that it may be used with various types of saw chains (e.g., chipper and chisel types), and for the different cutter link surfaces of those saw chains (i.e., depth gauges, gullets, and cutter teeth), and which may be used with saw chains of widely varying pitch;
(4) The development of a grinder in which the entire cutter tooth is ground at the same time, thereby not only increasing the efficiency of the grinding operation but also reducing wear to the grinding wheel;
(5) The provision of a saw chain grinder wherein the cutter tooth being ground is securely held in place during the grinding operation, thereby increasing the precision thereof; and
(6) The development of an automatic saw chain grinder in which indexing of the saw chain only occurs when the grinding which is in a raised, inactive position, thereby not only facilitating the aforedescribed versatility, but also increasing the accuracy of grinding operations while reducing the potentially debilitating wear to the saw chain inherent in some of the prior art proposals.